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Slightly Fewer Good Air Quality Days in 2017

Air quality in 9 out of 24 counties in Missouri improved in 2017 compared to 2016, while air quality in 14 declined. The data comes from the Air Quality Index Report maintained by the EPA , which contains data on the air quality of a number of Missouri counties going back to the early 1980s. For a fuller discussion of air quality and the data maintained by the EPA, or for a map of the counties, see my previous post.

Figure 1. Data source: Environmental Protection Agency.

Figure 1 at right show the percent of monitored days on which the Air Quality Index (AQI) was in the Good Range. The top graph is for a group of counties along the Mississippi River, the middle one is for a group of counties in the Kansas City-St. Joseph region, and the bottom one is for a widely scattered group of counties in neither of the other two groups. The charts represent every year from 2003-2017. In addition, they chart the data for 1983 and 1993 to give a long-term perspective.

(Click on figure for a larger view.)

Compared to 2016, the percentage of good air days increased in 9 out of the 24 counties. Most of the increases were small, but the percentage of good AQI days jumped by 32% in Stoddard County, by 23% in the Andrews County, by 19% in New Madrid County, and by 16% in the Jefferson County.

The percentage of good AQI days fell in 14 counties. In most cases the decline was small, In only Iron County was the decline as large as 10%.

Missouri’s 3 largest metropolitan areas, St. Louis, Kansas City, and Springfield had good air years in 2016, and counties associated with those cities all slipped in 2017.

In almost all Missouri counties the percentage of good air quality days was high in 2018. In no county was it below 60%, and it was 80% or above in 18 out of the 24 counties. As in previous years, the outstate group led in the percentage of good AQI days, which is expected because they don’t experience the concentration of pollution sources that large cities do.

In 2017, the City of St. Louis had the lowest percentage of good air days of any county in Missouri: 62%. St. Louis County had the second fewest, at 68%. In 1983, the percentage of good AQI days was 14% and 16% in those counties. St. Louis still has plenty of air quality challenges, but we’ve come a long way.

Clean air to breath should be everybody’s birthright. Looking at the chart, it is easy to see that over the long term, Missouri has greatly improved its air quality. It is just as easy to see, however, that we have more to do, especially in our large metropolitan areas.

Source:

Environmental Protection Agency. Air Quality Index Report. This is a data portal operated by the EPA. Data downloaded on 7/31/2017 from http://www.epa.gov/airdata/ad_rep_aqi.html.

Air Quality Update, 2017

I last looked at Missouri air quality data through the year 2016. This post begins a series to update the information through 2017. First will come an introduction to the Air Quality Index (AQI) criterion pollutants, then 2 posts on AQI trends over the years, then a post on which are the most important pollutants, and finally, a post on why air quality is important for human health.

Figure 1. The St. Louis Cathedral viewed from the Park Plaza on Black Tuesday (11/28/1939). Source: St. Louis Post-Dispatch.

Missouri has a notorious role in the annals of air quality, for 2 reasons. First, on November 28, 1939, a temperature inversion trapped pollutants in St. Louis; a thick cloud of dark smoke blanketed the city, blotting out the sun. The day came to be known as “Black Tuesday,” and it was one of the worst air quality events in recorded history. Figure 1 at right shows a view that day of the St. Louis Cathedral from (I think) the Park Plaza. More photos are available by searching on Google Images for “Black Tuesday St. Louis.” Second, St. Louis was one of 6 cities included in a 1993 study that conclusively showed a relationship between air pollution and mortality. St. Louis was the second most polluted city in that study. (Dockery et al, 1993)

Since then, many steps have been taken to reduce air pollution, and air quality has improved dramatically. Has the trend continued, or has the trend begun to backslide?

Since the 1980s the EPA has gathered air quality data from cities and counties in Missouri and maintained it in a national database. The following posts look at yearly data from 2003-2017. In addition, to give a longer term perspective, they include data for 1983 and 1993.

Figure 2. Counties for which the EPA reports air quality. Data source: Environmental Protection Agency.

The EPA data now includes 24 counties. In some of them, however, air quality has not been measured for the entire period. Figure 2 is map showing the locations of the 24 counties. They can be gathered into three groups: a group along the Mississippi River, a group in the Kansas City-St. Joseph Area, and a widely dispersed group that does not fall into either of the other two groups.

The EPA constructs an Air Quality Index (AQI) based on measurements of 6 criterion pollutants: particulates smaller than 2.5 micrometers particulates between 2.5 and 10 micrometers, ozone, carbon monoxide, nitrous oxide, and sulphur dioxide.

Particulates are tiny particles of matter that float around in the atmosphere. When we breathe, we inhale them, and if there are too many of them, they cause lung damage. There are 2 sizes: inhalable coarse particles have diameters between 2.5 and 10.0 micrometers, while fine particles have diameters less than 2.5 micrometers. How small is that? The diameter of a human hair is about 70 micrometers, so they are roughly 1/30 the width of a human hair. Figure 3 illustrates the size difference – these are really tiny particles. Recent evidence suggests that fine particles cause serious health problems; they get deep into the lungs, sometimes even getting into the bloodstream. (EPA 2015)

Figure 3. Size difference between human hair and PM2.5 particle.

Ozone is a highly corrosive form of oxygen. High in the atmosphere, we need ozone in order to absorb ultra-violet radiation. But at ground levels, it is corrosive to plants and animals, and too much of it can cause lung damage.

Sulphur dioxide smells like rotten eggs. Too much of it causes lung damage, and it also reacts with water vapor in the atmosphere to form sulphuric acid, one of the main ingredients of acid rain. A series of posts I wrote on background air pollution shows that background levels of sulphur dioxide have decreased over the last 30 years. However, concentrations of it can still build up and affect public health near emission sources.

Nitrous oxide is corrosive and reacts with ozone and sunlight to form smog. It is also one of the main causes of acid rain. Background levels in the atmosphere have decreased, but it, too, can build up locally near emission sources.

Perhaps the most important air pollutant of all, carbon dioxide, is not one of the criterion pollutants. It is not included in the AQI, and is not included in the discussion in the following posts. Carbon dioxide is the primary cause of climate change. I have written extensively on climate change in this blog, and interested readers can consult those posts by clicking on “Climate Change” at the top of the page or by looking for specific titles in the Table of Contents.

The biggest sources of air pollution are power plants, industrial facilities, and cars. These tend to concentrate in urban areas, but air quality can be a concern anywhere; some of Missouri’s air quality monitoring stations are located near rural lead smelters, for instance. Indeed, in my posts about the largest GHG emitting facilities in Missouri (here), I discovered that 7 out of 10 were located in rural areas.

In addition, weather plays an important role in air quality. On some days, weather patterns allow pollution to disperse, but on others they trap it, causing air quality to worsen. Hot, sunny summer days are of particular concern, although unhealthy air quality can happen any time. Black Tuesday was in November, after all.

The EPA has established maximum levels of each pollutant, and reports the number of days on which there are violations. The EPA also combines the pollutants into an overall Air Quality Index, or AQI, in order to represent the overall healthfulness of the air. The AQI is a number, but it does not have an obvious meaning. Suppose the median AQI is 75 – what does that mean? So the EPA has created six broad AQI ranges: Good, Moderate, Unhealthy for Sensitive Individuals, Unhealthy, Very Unhealthy, and Hazardous. The EPA reports a yearly AQI number and the number of days in which the AQI falls in each range.

In the following posts, I will update Missouri’s AQI, then the specific pollutants that seem to cause repeated problems.

Sources:

Dockery, Douglas W., Arden Pope III, Xiping Xu, John D. Spengler, James H Ware, Martha E. Fay, Benjamin G Ferris, and Frank E. Speizer. 1993. “An Association Between Air Pollution and Mortality in Six U.S. Cities.” The New England Journal of Medicine, 329 (4), pp. 1753-1759.

Environmental Protection Agency. Air Quality Index Report. This is a data portal operated by the EPA. Data downloaded on 7/31/2017 from http://www.epa.gov/airdata/ad_rep_aqi.html.

Environmental Protection Agency. 2015. Particulate Matter: Basic Information. Viewed online 3/23/2017 at https://www.epa.gov/pm-pollution.

St. Louis Post-Dispatch. Look Back: Smoky St. Louis. This is a gallery of photos concerning the 1930s smog problem in St. Louis. Photo purchased online from http://stltoday.mycapture.com/mycapture/folder.asp?event=896392&CategoryID=23105.

Wikipedia. 1939 St. Louis Smog. Viewed 11/6/15 at https://en.wikipedia.org/wiki/1939_St._Louis_smog.

Drought in American Southwest (Revised)

Revision: This is a revision of the post that appeared yesterday, 8/2/18. The Drought Monitor map issued 7/31/18 shows drought intensifying in Missouri, and extending to include most of the state. I’ve replaced the map in this revision with the newer one, and I’ve revised the text to include the new information.

Drought has one again gripped the American West and Southwest. Unfortunately, the wet winter of 2017 turned out to be a one-year reprieve. Perhaps the coming winter will be wet again, but for now, the regions are once again dry – in some cases, as dry as they have ever been since record-keeping began.

Figure 1. Source: Riganti, 2018.

Figure 1 shows the U.S. Drought Monitor for July 17, 2018. This map shows the Palmer Drought Severity Index for the United States. White areas are not in drought, colored areas are, and the darker the color, the worse the drought. It is easy to see that an “exceptional drought” has gripped portions of the Southwest, centered on the Four Corners Area where Colorado, New Mexico, Arizona, and Utah meet. Though the drought is most severe there, it has gripped much of the entire western United States.

Drought is primarily about soil moisture. Without moisture in the soil, crops wither and drinking water sources dry up. It is not feasible, however, to directly measure soil moisture across the entire country. The Palmer Drought Severity Index computes an estimate of soil moisture using temperature and precipitation data, and is the primary measure of drought used by the National Oceanographic and Atmospheric Administration.

 

Figure 2. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 2 shows the PDSI in June for the Southwest Climate Region (Arizona, Colorado, New Mexico, and Utah) from 1895 to 2018. Green columns represent years when it was wetter than average in June, orange columns when it was dryer than average. It is easy to see that green columns cluster to the left of the chart, and orange ones cluster to the right. In fact, of the most recent 19 years, 16 have been drier than average. This year, June was the second driest in the record, virtually as dry as it has ever been since record keeping began. The blue line shows the trend: the PDSI has decreased -0.23 per decade on average.

Ever since I wrote an extended series of posts on drought in California in 2015, this blog has followed the drought situation there. Plentiful snow during the winter of 2017 brought welcome relief, but the winter of 2018 was a big disappointment. Precipitation was below average, and the snowpack peaked well below normal (see here).

Figure 3. Source: Riganti, 2018.

As Figure 3 shows, California has not escaped the drought gripping most of the West. The most extreme drought is in the southeastern corner of the state. That is where the Imperial Valley is located, a region that supplies us with many of our fruits and vegetables. The farms there are mostly irrigated with water from the Colorado River, so local drought there is not a terrible worry for us here in Missouri. More on the Colorado River below, however.

 

 

 

 

Figure 4. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 4 shows that the PDSI for the state as a whole for June 2018, indicates a severe drought, but not an extreme one. The trend over time is clearly downward, however, and the continued dryness represents a long-term threat to the state’s water supply.

 

 

 

 

 

Figure 5. Source: California Department of Water Resources, 2018.

As Figure 5 shows, California’s reservoirs are moving into deficit. They have been fuller than average for most of the time since the winter of 2017, but now three of the biggest and most important, Trinity Lake, Lake Shasta, and Lake Oroville, are below average for this date. In the chart, the yellow bars represent the maximum capacity of each reservoir, the blue bars the current level, and the red line the average for this date. Lake Oroville has not yet fully recovered from the near disaster in 2017 that caused managers to lower the lake level to prevent a collapse of the dam(see here).

 

 

 

 

 

 

 

Figure 6. Source: Lake Mead Water Database, 2018.

Readers who have been following this blog know that California, Arizona, Nevada, Utah, New Mexico, and even Mexico depend on water from the Colorado River, and that Lake Mead is the large reservoir that holds the water for all of those states. You also know that water withdrawals from Lake Mead have exceeded inputs for many years, and the level of water in the lake has been relentlessly dropping. One study went so far as to predict that Lake Mead had a 50% chance of going dry by 2021. (Barnett and Pierce, 2008. See here for a fuller discussion California’s water resources.) Figure 6 shows the level of the lake for the past 3 years. The green line shows 2016, the red line 2017, and the blue line the year-to-date in 2018. Notice that the chart begins October 1, which is the official start of the water year. The wet winter of 2017 replenished the lake a little bit, but you can see that the current drought is causing it to drop again. Lake Mead is only 38% full, and Lake Powell, the large reservoir upstream from Lake Mead, is only 51% full. These low levels do not represent an immediate existential threat, but if dry conditions persist, they will before too many years pass.

 

Figure 7. Source: National Oceanographic and Atmospheric Administration, 2018.

The most important source of Missouri’s water is the Missouri River (see here). As Figure 7 shows, precipitation in the Northern Rockies and Plains Climate Region was slightly above average for the first 6 months of 2018. Statistics for the reservoirs along the Missouri show that they are at or near maximum storage. In fact, since part of their mission is flood control, several of them are higher than desired for that purpose. (U.S. Army Corps of Engineers, 2018)

Going back to Figure 1, however, you can see that the drought over the West has expanded to include Missouri, and it is especially severe in the northwestern part of the state. In St. Joseph, for instance, July brought 1.10 inches of rain, compared to 5.19 inches in an average July. In addition, since January 1, St. Joseph experienced 326 more heating degree days than average, an increase of 43%. That translates, on average, to a daily increase 1.8°F. (I arrived at this number by dividing the excess in heating degree days by the number of days.) Drought is as much a result of increased temperature as it is of reduced precipitation. Even if precipitation remains constant, increased temperature causes the ground to dry out more quickly, intensifying drought.

Because the reservoirs along the Missouri are relatively full, this drought will impact agriculture more than it will impact drinking water, unless your drinking water comes from wells. Drought can impact the availability of ground water to seep into wells, especially if they are shallow.

Climate projections for Missouri do not project a large decrease in precipitation. They tend to project that precipitation will remain about the same, or possibly increase slightly. Temperature, however, will rise, leading to a potential increase in the frequency of damaging drought. The real concern, however, is that the drought in the American West might not be not a temporary weather phenomenon, but, instead, a permanent change in climate. Modelers predict that climate change will cause just such a change Could it be occurring already?

Sources:

Barnett, Tim, and David Pierce. 2008. “When Will Lake Mead Go Dry?” Water Resources Research, 44, W03201. Retrieved online at http://www.image.ucar.edu/idag/Papers/PapersIDAGsubtask2.4/Barnett1.pdf.

Lake Mead Water Database. 2018. Lake Mead Daily Water Levels, Last 3 Water Years. Downloaded 7/19/2018 from http://graphs.water-data.com/lakemead.

National Oceanographic and Atmospheric Administration. 2018. Climate-at-a-Glance. Data downloaded 2018-07-19 from https://www.ncdc.noaa.gov/cag.

Riganti, Curtis. 2018. U.S. Drought Monitor, July 17, 2018. National Drought Mitigation Center. Downloaded 7/19/2018 from http://droughtmonitor.unl.edu.

U.S. Army Corps of Engineers, Missouri River Basin Water management. 2018. Mainstem and Tributary Reservoir Bulletin, 7/18/2018. Viewed online 7/19/2018 at http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/MRBWM_Reservoir.pdf.

Drought in American West and Southwest

Drought has one again gripped the American West and Southwest. Unfortunately, the wet winter of 2017 turned out to be a one-year reprieve. Perhaps the coming winter will be wet again, but for now, the regions are once again dry – in some cases, as dry as they have ever been since record-keeping began.

Figure 1. Source: Riganti, 2018.

Figure 1 shows the U.S. Drought Monitor for July 17, 2018. This map shows the Palmer Drought Severity Index for the United States. White areas are not in drought, colored areas are, and the darker the color, the worse the drought. It is easy to see that an “exceptional drought” has gripped portions of the Southwest, centered on the Four Corners Area where Colorado, New Mexico, Arizona, and Utah meet. Though the drought is most severe there, it has gripped much of the entire western United States.

Drought is primarily about soil moisture. Without moisture in the soil, crops wither and drinking water sources dry up. It is not feasible, however, to directly measure soil moisture across the entire country. The Palmer Drought Severity Index computes an estimate of soil moisture using temperature and precipitation data, and is the primary measure of drought used by the National Oceanographic and Atmospheric Administration.

 

Figure 2. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 2 shows the PDSI in June for the Southwest Climate Region (Arizona, Colorado, New Mexico, and Utah) from 1895 to 2018. Green columns represent years when it was wetter than average in June, orange columns when it was dryer than average. It is easy to see that green columns cluster to the left of the chart, and orange ones cluster to the right. In fact, of the most recent 19 years, 16 have been drier than average. This year, June was the second driest in the record, virtually as dry as it has ever been since record keeping began. The blue line shows the trend: the PDSI has decreased -0.23 per decade on average.

Ever since I wrote an extended series of posts on drought in California in 2015, this blog has followed the drought situation there. Plentiful snow during the winter of 2017 brought welcome relief, but the winter of 2018 was a big disappointment. Precipitation was below average, and the snowpack peaked well below normal (see here).

Figure 3. Source: Riganti, 2018.

As Figure 3 shows, California has not escaped the drought gripping most of the West. The most extreme drought is in the southeastern corner of the state. That is where the Imperial Valley is located, a region that supplies us with many of our fruits and vegetables. The farms there are mostly irrigated with water from the Colorado River, so local drought there is not a terrible worry for us here in Missouri. More on the Colorado River below, however.

 

 

 

 

Figure 4. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 4 shows that the PDSI for the state as a whole for June 2018, indicates a severe drought, but not an extreme one. The trend over time is clearly downward, however, and the continued dryness represents a long-term threat to the state’s water supply.

 

 

 

 

 

Figure 5. Source: California Department of Water Resources, 2018.

As Figure 5 shows, California’s reservoirs are moving into deficit. They have been fuller than average for most of the time since the winter of 2017, but now three of the biggest and most important, Trinity Lake, Lake Shasta, and Lake Oroville, are below average for this date. In the chart, the yellow bars represent the maximum capacity of each reservoir, the blue bars the current level, and the red line the average for this date. Lake Oroville has not yet fully recovered from the near disaster in 2017 that caused managers to lower the lake level to prevent a collapse of the dam(see here).

 

 

 

 

 

 

 

Figure 6. Source: Lake Mead Water Database, 2018.

Readers who have been following this blog know that California, Arizona, Nevada, Utah, New Mexico, and even Mexico depend on water from the Colorado River, and that Lake Mead is the large reservoir that holds the water for all of those states. You also know that water withdrawals from Lake Mead have exceeded inputs for many years, and the level of water in the lake has been relentlessly dropping. One study went so far as to predict that Lake Mead had a 50% chance of going dry by 2021. (Barnett and Pierce, 2008. See here for a fuller discussion California’s water resources.) Figure 6 shows the level of the lake for the past 3 years. The green line shows 2016, the red line 2017, and the blue line the year-to-date in 2018. Notice that the chart begins October 1, which is the official start of the water year. The wet winter of 2017 replenished the lake a little bit, but you can see that the current drought is causing it to drop again. Lake Mead is only 38% full, and Lake Powell, the large reservoir upstream from Lake Mead, is only 51% full. These low levels do not represent an immediate existential threat, but if dry conditions persist, they will before too many years pass.

 

Figure 7. Source: National Oceanographic and Atmospheric Administration, 2018.

The situation is different for Missouri. The most important source of water in our state is the Missouri Rivers (see here). Going back to Figure 1 above, you can see that drought is not severely impacting most of the region drained by the Missouri. As Figure 7 shows, precipitation in the Northern Rockies and Plains Climate Region was slightly above average for the first 6 months of 2018. Statistics for the reservoirs along the Missouri show that they are at or near maximum storage. In fact, since part of their mission is flood control, several of them are higher than desired for that purpose. (U.S. Army Corps of Engineers, 2018)

The real concern is that the drought in the American West might not be not a temporary weather phenomenon, but, instead, a permanent change in climate. Modelers predict that climate change will cause just such a change, could it be occurring already?

Sources:

Barnett, Tim, and David Pierce. 2008. “When Will Lake Mead Go Dry?” Water Resources Research, 44, W03201. Retrieved online at http://www.image.ucar.edu/idag/Papers/PapersIDAGsubtask2.4/Barnett1.pdf.

Lake Mead Water Database. 2018. Lake Mead Daily Water Levels, Last 3 Water Years. Downloaded 7/19/2018 from http://graphs.water-data.com/lakemead.

National Oceanographic and Atmospheric Administration. 2018. Climate-at-a-Glance. Data downloaded 2018-07-19 from https://www.ncdc.noaa.gov/cag.

Riganti, Curtis. 2018. U.S. Drought Monitor, July 17, 2018. National Drought Mitigation Center. Downloaded 7/19/2018 from http://droughtmonitor.unl.edu.

U.S. Army Corps of Engineers, Missouri River Basin Water management. 2018. Mainstem and Tributary Reservoir Bulletin, 7/18/2018. Viewed online 7/19/2018 at http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/MRBWM_Reservoir.pdf.

The First Half of 2018 Was Hot, but Not Record-Breaking

Figure 1. Source: National Oceanographic and Atmospheric Administration, 2018.

The first half of the year was hot across the USA, but not record-breaking. So says data published by the National Oceanographic and Atmospheric Administration, on their Climate-At-A-Glance data portal.

Figure 1 shows the average temperature across the 48 contiguous states for the months January – June. Nationwide, the first half of 2018 was the 13th hottest on record. There is a lot of variation from year-to-year, but the data show 4 distinct periods: at the beginning of the 20th Century, the average temperature was lower. During the 1930s-1950s, it was higher. From the 1960 to about 1980, it was cooler again, but not as cool as at the turn of the century. Then, beginning about 1980, the temperature began an upward trend. This upward trend is larger than any other trend in the record, due to global warming.

For larger view, click on figure.

Figure 2. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 2 shows the average temperature in Missouri for the months January – June. The first half of 2018 was the 93rd hottest on record across Missouri (out of 124 years). If you look more closely, the data reveal that May and June have been extremely hot, but the average across the period is lowered by the fact that we had an extraordinarily cool April – the 2nd coolest on record.

 

 

 

 

 

 

Figure 3. Data source: Hayhoe et al., 2003; Weather Underground, 2018.

Since the end of April, it has been hot; we’ve had a long stretch of days with the temperature above 90. In Missouri, May – June were the hottest on record. If climate change projections are correct, however, it’s nothing compared to what’s coming by the end of the century. Climate modelers have projected that under the high emissions scenario (which we continue to follow), by the end of the century the average number of days each summer when the high temperature reached above 90°F will triple, from 36 to 105. There will be 43 days above 100, the predict. (See here.) To try to figure out what that meant, I put a 105-day stretch on a calendar, and discovered that it would stretch from mid-June through the final weeks of September. I’ve reproduced that calendar as Figure 3. Dates projected to be above 90 are in orange, dates projected to be above 100 are in red. For comparison, I’ve marked on it the days in 2018 when the temperature was actually above 90°F in yellow, and dates when the temperature topped out below 90 in white. Dates in black had not yet occurred when the graphic was created (7/15/18).

You can see that we have a long way to go to equal what is predicted for us by the end of the century.

In terms of precipitation, the first half of 2018 was very close to average across Missouri (Figure 4). Across the Contiguous USA, it was just a touch above average (Figure 5). However, the averages do not tell the full story. After suffering a severe multi-year drought, the American West experienced a wet winter in 2017, but dry conditions returned in 2018. More on this in the next post, but Figure 6 shows that a drought centered on the Four Corners Area has once again gripped much of the West.

Figure 4. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 5. Source: National Oceanographic and Atmospheric Administration, 2018.

 

 

 

 

 

 

 

 

Figure 6. Source: Riganti, 2018.

All-in-all, for the first half of the year, the temperature and precipitation pattern for Missouri and the Contiguous USA were consistent with climate change predictions contained in the reports of the Intergovernmental Panel on Climate Change and the U.S. Global Change Research Program. Not every year will be a record year, they predict, but the trend will be towards warmer temperatures. Changes in precipitation will vary by region. For Missouri the reports predict no change or a slight increase in the average annual amount of precipitation.

Extremely hot days are associated with a number of undesirable effects, including increased deaths from heat exhaustion, increased respiratory illness, and reduced productivity. For a fuller discussion, see here.

Sources:

Hayhoe, K, J VanDorn, V. Naik, and D. Wuebbles. 2009. “Climate Change in the Midwest: Projections of Future Temperature and Precipitation.” Technical Report on Midwest Climate Impacts for the Union of Concerned Scientists. Downloaded from http://www.ucsusa.org/global_warming/science_and_impacts/impacts/climate-change-midwest.html#.VvK-OD-UmfA.

National Oceanographic and Atmospheric Administration. 2018. Climate-at-a-Glance. Data downloaded 2018-07-19 from https://www.ncdc.noaa.gov/cag/national/time-series.

Riganti, Curtis. 2018. U.S. Drought Monitor, July 17, 2018. National Drought Mitigation Center. Downloaded 7/19/2018 from http://droughtmonitor.unl.edu.

Weather Underground. St. Louis Downtown, IL >> History >> Monthly. Downloaded 2018-07-19 from https://www.wunderground.com/history/monthly/us/il/cahokia/KCPS/date/2018-7?cm_ven=localwx_history.

Disinfectant Byproducts Are the Most Common Water System Violations

In 2016, there were 2,733 public water supply systems in Missouri. In the previous post, I reported that 94.7% of the population received water from suppliers that had no violations of safe drinking water standards during the year (it has decreased from 95.7% in 2012). This means that 5.3% of the population was served by systems that did have a violation. As Missouri’s population in 2016 was 2,093,000, that means that almost 111,000 people were served water systems that had a violation during the year. This post looks into the nature of the violations.

In 2007 and 2010 there was an increase in the population affected by a violation. The cause in 2007 was an error in backwashing a filter at the Missouri American Water Company South Plant in St. Louis County. The error caused a spike in turbidity that lasted four minutes. During that time the water reached an estimated 24,578 customers, though no reports of illness were associated with this event. Even though only some customers were affected, federal documentation rules require that the entire service population be reported as exposed. In 2010, “the same phenomenon happened again.” (2012 Annual Compliance Report of Missouri Public Drinking Water, p. 4)

A violation does not indicate that public health was affected, but it creates the potential for a public health impact to occur. For this reason, violations are important administrative markers. The DNR monitors two broad kinds of violations. Water contaminants (chemicals and bacteria) can exceed their respective maximum concentration levels (health-based standards), or a water system can fail to meet adequate administrative standards (most often not performing and reporting the water quality tests required by law).

Figure 1 at right shows the percentage of the population served by community water systems that had different types of health-based violations in 2016. Violations of the Stage 1 & 2 DBP Rule were by far the most common, affecting about 3% of the population. (In the chart, Excel has rounded to the nearest full percent.) Figure 2 compares the data for 2013 and 2016.

(For larger view, click on figure.)

Figure 1. Data source: Missouri Department of Natural Resources, 2016.

Figure 2. Data source: Missouri Department of Natural Resources, 2016.

 

 

 

 

 

 

 

 

 

 

In previous years, the most common type of violation had to due with coliform bacteria. The text of the report indicates that in 2016 coliform contamination continued to represent the most common kind of violation. However, as shown in Figures 1 and 2, violations of the Stage 1 & 2 DBP Rule affected more of the population than did coliform contamination. Let me explain what this means.

Coliform bacteria are a family of bacteria that live naturally in the soil, and which also live naturally in the guts of many animals, including humans. Consequently, it is not uncommon for some coliform bacteria to get into water supplies. Most coliform bacteria are safe, but a few species of coliform bacteria (including some E. coli) can cause illness in humans. In addition, because they live in great numbers in the guts of humans and animals, their presence in large numbers serves as a sign of fecal contamination. Human and animal feces contain many species of harmful bacteria, and the presence of too many coliform bacteria serves as a marker that these other bacteria might be present, too.

Over the years, the EPA has lowered the maximum allowable level of coliform bacteria concentration in drinking water, and water systems have had to increase their treatment of the water to kill the bacteria. The treatment usually occurs in stages. Unfortunately water often contains organic matter, such as algae or dissolved plant material. If the water treatment is not done properly, the chemicals used to kill the bacteria react with the contaminants to form byproducts that can also be harmful. The Stage 1 & 2 DBP (Disinfectants and Disinfection ByProducts) Rule requires water systems to monitor the level of such byproducts in their water. Thus, it may be because water systems are using additional treatment to kill bacteria that decreasing coliform contamination and increasing violations of the Stage 1 & 2 DBP rule are occurring.

The presence of E. Coli or of other species of coliform bacteria remains the most serious violation, in the Department’s opinion. Thus, the presence of either results in a boil order. All water systems in Missouri are required to test for E. Coli. Nineteen systems received boil orders in 2016. That number has been moving mostly sideways since 2012, but represents a decrease from 32 in 2011. Most lasted for a few days up to two weeks, but some lasted for several months.

Seventy-four systems had chemical violations, almost all for trihalomethanes . Trihalomethanes are water treatment byproducts. They form if disinfectants used to treat the water (chlorine or bromine) react with matter that may be present in the water (e.g. decaying vegetation).

Eleven systems had violations involving excess radiological contaminants (down from 14 systems in 2012 and 16 systems in 2011). The problems came from several radiological elements, see the report for full details.

In 2016, 7 water systems had Surface Water Rule violations, the same as in 2013. All of the violations were for combined filter effluent turbidity. Systems must filter surface water to remove cryptosporidium, a parasite that causes diarrhea, and a violation of the turbidity rule means the filtering may not be adequate to remove the parasite.

As noted above, some of violations can be quite brief, and the threat they represent to public health can be small. However, the DNR puts a special focus on water systems that repeatedly fail to meet monitoring standards, and on those with a routine sample that tests positive for coliform, but which fail to submit follow-up or repeat samples as required.

As reported in the previous post, 38 water systems were listed as having had three or more major monitoring violations in 2016 (up from 27 systems in 2013). Many of them were in violation for many months. Figure 3 shows the list. Only 6 water systems had water that tested positive for excess coliform bacteria, but failed to provide the required follow-up samples for testing. This represents a decrease from 47 systems in 2013. Figure 4 shows the list.

Figure 3. Source: Missouri Department of Natural Resources, 2016.

Figure 4. Source: Missouri Department of Natural Resources, 2016.

 

 

 

 

 

 

 

 

 

 

 

 

Sources:

Missouri Department of Natural Resources. 2013 Annual Compliance Report of Missouri Public Drinking Water Systems. https://dnr.mo.gov/env/wpp/fyreports/index.html. Published 2014-11-18.

Missouri Department of Natural Resources. 2016. Annual Compliance Report of Missouri Public Water Systems. Downloaded 5/11/2018 from https://dnr.mo.gov/env/wpp/fyreports/index.html.
Missouri Census Data Center. Population Estimates for Missouri. Viewed online 6/28/2018 at http://mcdc.missouri.edu/trends/estimates.shtml.
Wikipedia contributors. (2018, May 15). Trihalomethane. In Wikipedia, The Free Encyclopedia. Retrieved 22:26, July 5, 2018, from https://en.wikipedia.org/w/index.php?title=Trihalomethane&oldid=841446641

Most Public Water Systems Met All Health-Based Regulations in 2016

The previous post reported that the Census of Missouri Public Water Systems – 2016 found 2,733 public water systems in Missouri, of which 2,720 were active. This post looks at Missouri’s 2016 Annual Compliance Report of Missouri Public Drinking Water Systems. It is the most recent summary report on Missouri’s public water systems. Additional detail about specific systems can be found in reports published by the systems themselves.

A public water system is one that provides water to at least 15 service connections, or to an average of at least 25 people for at least 60 days each year. Community Systems (CWS) supply water to the same population year-round. Non-Transient Non-Community Water Systems (NTNCWS) supply water to at least 25 of the same people at least 6 months per year, but not year-round. An example might be a school that has its own water system. Transient Non-Community Water Systems (TNCWS) provide water in places where people do not remain for long periods of time. Examples might include gas stations or campgrounds that have their own water systems.

The amount of treatment that water must receive differs depending on the source of the water. Surface water and underground water under the direct influence of surface water are more vulnerable to contamination, so they receive more treatment. Underground water from aquifers not under the direct influence of surface water tend to contain water that is heavily filtered by the rock through which it seeps. Sometimes, the seepage is so slow that the water is old, predating most forms of modern contamination.

Figure 1. Source: Missouri Department of Natural Resources, 2016.

Figure 2. Source: Missouri Department of Natural Resources, 2016.

 

 

 

 

 

 

 

 

Figure 1 shows the percentage of population served by community water systems that meet all health-based requirements by year. Figure 2 shows the number of violations involving E. Coli or acute contamination levels. Non-compliance can result from many factors from broken pipes, to human error, to systems that are inadequate in the first place. The EPA goal is for 95% of the public water systems in a state to have no health-based violations in a year. In 2016, Missouri had 94.7% compliance. That is close to the goal, but it is a decrease from over 95% in 2013. The chart shows no general trend, but in some years the compliance rate appears to slip significantly. The last 3 years have all been below the EPA goal.

The number of violations for E. coli and acute MCL violations (maximum contaminant level violations – also mostly due to coliform contamination) peaked in 2008 and had another bad year is 2011. Since 2012, it has mostly been moving sideways. In 2016, there were 19 violations.

Ninety-four-point-seven percent is a high mark – you would have been happy to score 94.7% on tests at school, wouldn’t you? Since Missouri’s population in 2016 was 2,093,000, however, it means that water systems serving almost 111,000 people had a health-based violation. (Missouri Census Data Center)

In 2016, 38 public water systems had 3 or more “major monitoring violations” of the rules to protect against coliform contamination. That is an increase from 27 in 2013. Monitoring violations are a concern because hinders the Department of Natural Resources’s ability to determine if the drinking water is safe, especially if the monitoring violation occurs multiple times.

In 2016, however, there were only 6 major “repeat monitoring violations,” down from 41 in 2013. A repeat monitoring violation occurs when If a routine sample from a public water system tests positive for coliform bacteria, then the system is required to submit a second test to confirm the finding, and to conduct follow up testing to ensure that the problem is eliminated. A repeat monitoring violation occurs when the system fails to submit the repeat testing or follow up testing.

None of these violatios mean that people were actually sickened, the report does not address that issue. It does mean, however, that a potential vulnerability occurred, and that continuing work needs to be done to ensure that Missourians have safe drinking water.

The next post will look into the nature of the violations that occurred.

Sources:

Missouri Census Data Center. Population Estimates for Missouri. Viewed online 6/28/2018 at http://mcdc.missouri.edu/trends/estimates.shtml.

Missouri Department of Natural Resources. 2016. Annual Compliance Report of Missouri Public Water Systems. Downloaded 5/11/2018 from https://dnr.mo.gov/env/wpp/fyreports/index.html.

Census of Public Water Systems, 2018

Each year the Missouri Department of Natural Resources publishes the Census of Missouri Public Water Systems. I reported on the 2013 census here, and the 2014 census here, and the 2015 census here. This post reports on the 2016-2018 censuses. The census provides basic information about the number and type of public water systems in the state, plus information on each system that includes the source of its water, the type of treatment it gives the water, and a chemical analysis of the water that covers 16 inorganic chemicals.

The EPA defines a public water system as one that provides water for human consumption to at least 15 service connections or that serves an average of at least 25 people for at least 60 days a year. It classifies public water systems in three categories. Community Water Systems (CWS) supply water to the same population year-round. Non-Transient Non-Community Water Systems (NTNCWS) supplies water to at least 25 of the same people at least 6 months per year, but not year-round. An example might be a school that has its own water system. A Transient Non-Community Water System (TNCWS) provides water in a place where people do not remain for long periods of time. Examples might include gas stations or campgrounds that have their own water systems. Not included in the report are private systems, such as a privately owned well that provides water only to its owner.

Table 1 shows the number of public water systems in Missouri by category. In 2018 there were 2,732 public water systems in Missouri, about 52% of which were community water systems. The numbers have not changed greatly over the years.

Table 1.

Table 1. Data source: Missouri Department of Natural Resources, 2013 through 2018.

A primary water system is one that obtains water from a well, infiltration gallery, lake, reservoir, river, spring, or stream. A secondary water system is one that obtains its water from an approved water system, and distributes it to consumers. (Missouri 10 CSR 60-2015, Definitions) For instance, in 2018 the St. Louis City Public Water System was a primary system. It obtained 100% of its water from surface water supplies, and treated the water itself. On the other hand, the Kirkwood Public Water System was a secondary system. It purchased 100% of its water from Missouri American Water, which treated the water before selling it to Kirkwood. Kirkwood only distributes the water.

In 2018, about 78% of Missouri public water systems were primary systems, and they served about 79% of the population. Table 2 shows the number of systems by water source, and Table 3 shows the population served by each type.

Table 2.

Table 2. Data source: Missouri Department of Natural Resources, 2013 through 2018.

Table 3.

Table 3. Data source: Missouri Department of Natural Resources, 2013 through 2018.

Groundwater means groundwater that is not directly influenced by the surface water above it. The groundwater is isolated from surface groundwater by thick layers of rock or sediment that filter the ground water before it reaches the groundwater aquifer. Such groundwater is often considered less vulnerable to pollution by chemicals and organic waste. Groundwater Under Direct Influence refers to groundwater that is not protected from the surface water above it, and which consequently contains groundwater contaminants, such as chemicals, insects, microorganisms, algae, or turbidity. This kind of water requires more extensive treatment before it is fit for use. So does surface water. Groundwater is a limited resource, however, that sometimes takes hundreds, if not thousands, of years to percolate into underground aquifers. Overuse can deplete it. (See here.)

In 2018, groundwater systems constituted 84.5% of the total number of systems, but they served only 37.1% of the population. On the other hand, surface systems constituted 15.2% of the systems, but served 62.4% of the population. Table 3 shows the population served by water source.

Most of the water systems in Missouri source their water from groundwater, only a few from ground water under direct influence. However, the source serving the largest population is surface water. Specifically, the Missouri River is the water source for much of the Kansas City and St. Louis metropolitan areas. More than half of Missouri’s population is served by water either from the Missouri River Alluvial Aquifer or water from the river itself.

Source:

Missouri Department of Natural Resources. 2013. 2013 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2014. 2014 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2015. Census of Missouri Public Water Systems, 2015. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2016. 2016 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2017. 2017 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2018. 2018 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri’s Major Power Outages

For several posts I have been reporting on the bulk power grid in the United States. The Grid, as I have been calling it, delivers high voltage electricity from generating stations to local distributors. The local distributors step the voltage down and deliver the electricity to individual customers. Ameren, for instance, claims to own 7,500 miles of transmission lines (Ameren, undated), while Great Plains Energy (parent of Kansas City Power & Light) claims to own 3,600 miles (Westar & Great Plains Energy, 2018).

In the past, relatively small problems at specific locations on The Grid have cause cascading failures that left tens of millions of customers without power. The North American Reliability Corporation (NERC) publishes an annual reliability report, in which they evaluate the kinds of problems that been related to those types of grid collapses: electricity demand, generating capacity, transmission capacity, and operating procedures. I reported on the conclusions of that report in the last 2 posts.

Missouri has not been caught-up in those grid collapses. Widespread power outages in Missouri have been caused by severe weather. Both summer and winter storms have brought down large parts of local transmission grids.

For security purposes, the U.S. Department of Energy requires utilities to file reports of electric incidents and emergencies affecting The Grid. These reports cover much of the local distribution system, as well as the bulk power system we have been discussing in previous posts. These reports are known as OE-417 reports. They include major power outages, but they also cover things like vandalism and sabotage, even if they don’t result in a loss of power to any customers. Large utilities are required to submit the reports, but smaller utilities must file only “as appropriate.” (Department of Energy, undated.)

Table 1. Data source: Inside Energy, 2014, and U.S. Department of Energy, undated.

Inside Energy, an organization that studies the reliability of The Grid, put together a database from these reports that covers the years 2000-2014 (Inside Energy, 2014). To that database, I have added the Department of Energy data for the years 2015, 2016, and 2017, creating a database that lists events from 2000-2017. I then selected only those events in which the area affected included “Missouri,” “St. Louis,” or “Kansas City.” It is as comprehensive a database of events affecting Missouri as I can put together, though given the limits in the reporting requirements, it is not completely comprehensive. It probably catches all large power outages, but may not capture some of the smaller ones.

For a widespread power outage, what is your definition of widespread? Table 1 lists the individual events, gives a brief description of the kind of event it was, and shows how many customers were affected. In reading this table, be sure to note that many of the events affected more than one state. Thus, some of the customers affected may have been in other states.

(Click on table for larger view.)

While there have been large events, none of them match the scale of the events that plunged tens of millions of customers into darkness in the Northeast. The largest event occurred in 2006, when severe summer storms caused 2,500,000 customers to lose power in the Greater St. Louis Area (including Illinois). Anybody remember that one? I sure do. While that was less than 1/10th of the number of people affected by the Great Northeast Blackout of 2003, it was a very major event!

Figure 1. Data source: Inside Energy, 2014, and U.S. Department of Energy, undated.

The table shows 30 events overall, but none prior to 2002, and none from 2003-2005. Was that really the case? I don’t know. I have previously reported on the dollar value of weather-related damage in Missouri, and while 2004 and 2005 were very low damage years, 2000, 2001, and 2003 were not (see here). Thus, one wonders if there are holes in the data. Overall, there were on average 1.67 electrical disturbances per year.

Figure 1 charts the number of disturbances per year. While there is a lot of yearly variation (the weather is always variable from year-to-year) there is a clear trend toward an increased number of outages per year.

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Figure 2. Data source: Inside Energy, 2014, and U.S. Department of Energy, undated.

Figure 2 charts the number of customers affected per year. The chart is dominated by the very large event of 2006, but even if you eliminate that one year, the chart does not seem to show a clear trend toward an increased number of customers affected.

Given that damage from weather-related events in Missouri has increased over time, and that the number of outages has increased over time, one is tempted to guess that utilities have made progress in protecting at least some parts of their distribution networks from large scale outages. One can’t be sure from this data, however, it would be an interesting topic for additional research.

The Missouri State Emergency Management Agency prepared a Missouri State Hazard Mitigation Plan in July of 2013, and the analysis in that plan suggests that power outages are not inconsequential. Many essential services rely on electrical power. For instance, many of the life-support systems in hospitals require electricity, pumps that deliver drinking water run on electricity, and the refrigerators that keep our food from spoiling do, too. Further, I have reported previously on deaths caused by extreme heat waves, and some of those deaths result from the loss of air conditioning due to power outages.

The Agency estimated that total loss of electric power results in dollar damages of $126 per person affected, per day. Multiplying that by the estimated population of each county, their estimates ranged from a low of $27,355 per day in Worth County to a high of $12,5865,820 per day in St. Louis County. (Missouri State Emergency Management Agency, 2013, pp. 3.542-3.547) These are damages that could mount-up very quickly.

Thus, the electrical grid is something we all use every single day, and our very lives depend on it. It is a huge, complex, interconnected machine. Its reliability seems an issue vital to our lives and to our security.

Sources:

Ameren. Undated. Ameren Facts and Figures. Viewed online 5/21/2018 at https://www.ameren.com/about/facts.

Inside Energy. 2014. Grid Disruption 00 14 Standardized. Downloaded 5/9/2018 from https://docs.google.com/spreadsheets/d/1AdxhulfM9jeqviIZihuODqk7HoS1kRUlM_afIKXAjXQ/edit#gid=595041757. This is a Google Spreadsheet linked to Data: Explore 15 Years of Power Outages. Viewed online at http://insideenergy.org/2014/08/18/data-explore-15-years-of-power-outages.

Missouri Satate Emergency Management Agency. 2013. Missouri State Hazard Mitigation Plan, July 2103. Downloaded 5/24/2018 from https://sema.dps.mo.gov/docs/programs/LRMF/mitigation/MO_Hazard_Mitigation_Plan_2013.pdf.

United States Department of Energy. Undated. Electric Disturbance Events (OE-417). Viewed online 2018-06-04 at https://www.oe.netl.doe.gov/oe417.aspx.

Westar Energy & Great Plains Energy. 2018. Merger to Form Leading Company: January 2018 Investor Update. Viewed 5/21/2018 at http://www.greatplainsenergy.com/static-files/b8b91848-48a6-4f88-8fd3-df3b59316b96.

Future Grid Resources in Missouri

In my last post I looked at the 2017 Long-Term Reliability Assessment issued by NERC, the North American Electric Reliability Corporation. In that post, I focused on a grid-wide perspective. In this post, I’ll offer a few conclusions in the report that pertain to Missouri.

In the northeastern USA, the largest power outages have been caused by relatively small failures at specific locations that caused underloads or overloads, which then cascaded into region-wide outages. They have affected tens of millions of customers. Consequently, the 2017 Long-Term Reliability Report focuses on the kinds of issues involved in those blackouts: electricity demand, generating capacity, transmission capacity, and operating procedures.

In Missouri, however, the largest power outages have been caused by storms that destroyed transmission lines, most of which are in the local transmission grid. (See Electrical Outages from Storms Increase.) The 2013 Long-Term Reliability Assessment does not cover the local transmission grid, and it does not seek to evaluate the potential for damaging storms. Thus, the findings of the report deal with important planning issues for The Grid in Missouri, but they don’t address the historical reasons for our power outages. I will look at weather-related power outages in Missouri in the next post.

Figure 1. Source: North American Reliability Corporation 2017.

The resource adequacy of Missouri’s grid depends on where you are. Some western portions of the state, including Kansas City, (see Figure 1) belong to the SPP reporting region (Southwest Power Pool). The SPP 10-year compound growth rate in demand for electricity is 0.56%. The anticipated reserve margin is projected to fall from 32.43% in 2018 to 19.85% in 2027, but remain well above NERC’s 12.00% target.

The central portion of the state belongs to the SERC-N reporting region (SERC Reliability Corporation–North). The SERC-N 10-year compound growth rate in demand for electricity is projected to be 0.38%. The anticipated reserve margin is projected to fall from 21.45% to 17.18% in 2027, still above NERC’s 15.00% target.

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Figure 2. MISO Projected Capacity Reserve. Source: National Electrical Reliability Organization 2017.

A portion of eastern Missouri belongs to the Midwest Independent Service Organization (MISO) reporting region, including the St. Louis Metropolitan Region. The MISO 10-year compound annual growth rate is 0.28%. Though starting at 19.23% in 2018, the reserve margin level will fall below the Reference Margin Level (15.80%) in 2023, and will reach 14.56% by 2027. In fact, despite projected growth in demand, generating resources are projected to decline slightly. Figure 2 shows a graphical representation of the projection, with anticipated reserve in dark blue (anticipated reserves are based on plans announced by utilities), and prospective reserve in light blue (prospective reserves are based on potential plans discussed by utilities, but not announced).

These conclusions are more hopeful than those reached in the 2013 Long-Term Reliability Report. The primary reasons are that demand growth is projected to slow, fewer power plant retirements are projected to occur, and utilities have become better at forecasting demand and outages. That notwithstanding, we have entered a period of uncertainty with regard to our national bulk electricity grid. A few years ago legislation made it mandatory for all participants in The Grid to participate in NERC, and it gave NERC regulations the force of law. These changes hold out the potential for increased reliability and improved operations. On the other hand, many factors combine to represent threats to the long-term reliability of The Grid: aging infrastructure, environmental regulations that will force the retirement of coal-fired generating capacity, the retirement of nuclear generating capacity that has reached the end of its useful life, new generating sources that provide constantly varying amounts of power to The Grid, and uncertainty surrounding demand side management programs.

Resource adequacy in western and central Missouri is projected to be adequate through 2027. In eastern Missouri, reserves are projected to fall below the target level by 2023, and continue to edge lower through 2027. I will look at weather-related power outages in Missouri in the next post.

Source:

North American Electric Reliability Corporation. 2013. 2013 Long-Term Reliability Assessment. http://www.nerc.com/pa/RAPA/ra/Reliability%20Assessments%20DL/2013_LTRA_FINAL.pdf.

North American Electrical Reliability Corporation. 2017. 2017 Long-Term Reliability Assessment. Downloaded 4/27/2018 from https://www.nerc.com/pa/RAPA/ra/Pages/default.aspx.